What kind of store selling plastic angle bar ? I looking for Home depo, Low"s. But I can't find plastic angle bar.?

Grainger has them

https://www.grainger.com/search?searchBar=true&sea...

Look online at Tek Supply. If I understand your question correctly, you're looking for a length of material that is like angle iron except in plastic.

Tek Supply carries such in different thickness and widths, so you should be able to put a finished corner on whatever it is you're working on. I've ordered a fair amount of the stuff myself, to put tough corners on commercial shower stalls. Use stainless steel hardware, or else cap the screw heads.

Hotel supply vendors offer it.

look online. they have thousands of products online that aren't in the physical store down the street